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This information has been developed and provided by an independent third-party source. Merck & Co., Inc. does not endorse and is not responsible for the accuracy of the content, or for practices or
standards of non-Merck sources.
ALERT: U.S. Boxed Warning
The FDA-approved labeling includes a boxed warning. See Warnings/Precautions section and/or refer to product labeling for additional detail.
Medication Safety Issues
Sound-alike/look-alike issues:
Levothyroxine may be confused with levofloxacin, liothyronine
Levoxyl® may be confused with Lanoxin®, Levaquin®, Luvox®
Synthroid® may be confused with Symmetrel®
To avoid errors due to misinterpretation of a decimal point, always express dosage in mcg (not mg).
Significant differences exist between oral and I.V. dosing. Use caution when converting from one route of administration to another.
Pronunciation
(lee voe thye ROKS een)
U.S. Brand Names
Index Terms
Generic Available
Yes: Excludes capsule
Canadian Brand Names
Pharmacologic Category
Use: Labeled Indications
Replacement or supplemental therapy in hypothyroidism; pituitary TSH suppression
Pregnancy Risk Factor
A
Pregnancy Considerations
Untreated maternal hypothyroidism may have adverse effects on fetal growth and development and is associated with higher rate of complications (spontaneous abortion, pre-eclampsia, stillbirth, premature delivery). Treatment should not be discontinued during pregnancy. TSH levels should be monitored during each trimester and 6-8 weeks postpartum. Increased doses may be needed during pregnancy.
Lactation
Enters breast milk/compatible
Breast-Feeding Considerations
Minimally excreted in human milk; adequate levels are needed to maintain normal lactation
Contraindications
Hypersensitivity to levothyroxine sodium or any component of the formulation; recent MI or thyrotoxicosis; uncorrected adrenal insufficiency
Warnings/Precautions
Boxed warnings:
• Weight reduction: See “Other warnings/precautions” below.
Disease-related concerns:
• Adrenal insufficiency: Use with caution in patients with adrenal insufficiency; symptoms may be exaggerated or aggravated.
• Cardiovascular disease: Use with caution and reduce dosage in patients with angina pectoris or other cardiovascular disease; chronic hypothyroidism predisposes patients to coronary artery disease.
• Diabetes: Use with caution in patients with diabetes mellitus and insipidus; symptoms may be exaggerated or aggravated.
• Myxedema: Use with caution in patients with myxedema; symptoms may be exaggerated or aggravated.
• Osteoporosis: Long-term therapy can decrease bone mineral density. Postmenopausal women and women using suppressive doses should receive the lowest dose necessary for clinical response.
Special populations:
• Elderly: Use with caution; may be more likely to have compromised cardiovascular function; decrease initial dose.
Dosage form specific issues:
• Levoxyl®: Product may rapidly swell and disintegrate causing choking or gagging (should be administered with a full glass of water); use caution in patients with dysphagia or other swallowing disorders.
Other warnings/precautions:
• Weight reduction: [U.S. Boxed Warning]: Thyroid supplements are ineffective and potentially toxic for weight reduction.
High doses may produce serious or even life-threatening toxic effects particularly when used with some anorectic drugs.
Adverse Reactions
Frequency not defined.
Cardiovascular: Angina, arrhythmia, blood pressure increased, cardiac arrest, flushing, heart failure, MI, palpitation, pulse increased, tachycardia
Central nervous system: Anxiety, emotional lability, fatigue, fever, headache, hyperactivity, insomnia, irritability, nervousness, pseudotumor cerebri (children), seizure (rare)
Dermatologic: Alopecia
Endocrine & metabolic: Fertility impaired, menstrual irregularities
Gastrointestinal: Abdominal cramps, appetite increased, diarrhea, vomiting, weight loss
Hepatic: Liver function tests increased
Neuromuscular & skeletal: Bone mineral density decreased, muscle weakness, tremor, slipped capital femoral epiphysis (children)
Respiratory: Dyspnea
Miscellaneous: Diaphoresis, heat intolerance, hypersensitivity (to inactive ingredients, symptoms include urticaria, pruritus, rash, flushing, angioedema, GI symptoms, fever, arthralgia, serum sickness, wheezing)
Levoxyl®: Choking, dysphagia, gagging
Drug Interactions
Bile Acid Sequestrants: May decrease the absorption of Thyroid Products. Risk C: Monitor therapy
CarBAMazepine: May decrease the serum concentration of Thyroid Products. Risk C: Monitor therapy
Estrogen Derivatives: May diminish the therapeutic effect of Thyroid Products. Risk C: Monitor therapy
Ferrous Sulfate: May decrease the serum concentration of Levothyroxine. Risk D: Consider therapy modification
Phenytoin: May increase the metabolism of Thyroid Products. Phenytoin may also displace thyroid hormones from protein binding sites. Risk C: Monitor therapy
Raloxifene: May decrease the absorption of Levothyroxine. Risk D: Consider therapy modification
Rifampin: May decrease the serum concentration of Thyroid Products. Risk C: Monitor therapy
Sodium Iodide I131: Thyroid Products may diminish the therapeutic effect of Sodium Iodide I131. Risk X: Avoid combination
Sucralfate: May decrease the serum concentration of Levothyroxine. Risk C: Monitor therapy
Theophylline Derivatives: Thyroid Products may increase the metabolism of Theophylline Derivatives. Exceptions: Dyphylline. Risk C: Monitor therapy
Vitamin K Antagonists (eg, warfarin): Thyroid Products may enhance the anticoagulant effect of Vitamin K Antagonists. Risk D: Consider therapy modification
Ethanol/Nutrition/Herb Interactions
Food: Taking levothyroxine with enteral nutrition may cause reduced bioavailability and may lower serum thyroxine levels leading to signs or symptoms of hypothyroidism. Soybean flour (infant formula), cottonseed meal, walnuts, and dietary fiber may decrease absorption of levothyroxine from the GI tract.
Storage
Store tablets and injection at room temperature of 15°C to 30°C (59°F to 86°F). Protect tablets from light and moisture.
Reconstitution
Dilute vial for injection with 5 mL normal saline. Reconstituted concentrations for the 200 mcg and 500 mcg vials are 40 mcg/mL and 100 mcg/mL, respectively. Shake well and use immediately after reconstitution; discard any unused portions.
Compatibility
Do not mix I.V. solution with other I.V. infusion solutions.
Mechanism of Action
Exact mechanism of action is unknown; however, it is believed the thyroid hormone exerts its many metabolic effects through control of DNA transcription and protein synthesis; involved in normal metabolism, growth, and development; promotes gluconeogenesis, increases utilization and mobilization of glycogen stores, and stimulates protein synthesis, increases basal metabolic rate
Pharmacodynamics/Kinetics
Onset of action: Therapeutic: Oral: 3-5 days; I.V. 6-8 hours
Peak effect: I.V.: 24 hours
Absorption: Oral: Erratic (40% to 80%); may be decreased by age and specific foods and drugs
Protein binding: >99%
Metabolism: Hepatic to triiodothyronine (active)
Time to peak, serum: 2-4 hours
Half-life elimination: Euthyroid: 6-7 days; Hypothyroid: 9-10 days; Hyperthyroid: 3-4 days
Excretion: Urine and feces; decreases with age
Dosage
Doses should be adjusted based on clinical response and laboratory parameters.
Oral:
Children: Hypothyroidism:
Newborns: Initial: 10-15 mcg/kg/day. Lower doses of 25 mcg/day should be considered in newborns at risk for cardiac failure. Newborns with T4 levels <5 mcg/dL should be started at 50 mcg/day. Adjust dose at 4- to 6-week intervals.
Infants and Children: Dose based on body weight and age as listed below. Children with severe or chronic hypothyroidism should be started at 25 mcg/day; adjust dose by 25 mcg every 2-4 weeks. In older children, hyperactivity may be decreased by starting with 1/4 of the recommended dose and increasing by 1/4 dose each week until the full replacement dose is reached. Refer to adult dosing once growth and puberty are complete.
0-3 months: 10-15 mcg/kg/day
3-6 months: 8-10 mcg/kg/day
6-12 months: 6-8 mcg/kg/day
1-5 years: 5-6 mcg/kg/day
6-12 years: 4-5 mcg/kg/day
>12 years: 2-3 mcg/kg/day
Adults:
Hypothyroidism: 1.7 mcg/kg/day in otherwise healthy adults <50 years old, children in whom growth and puberty are complete, and older adults who have been recently treated for hyperthyroidism or who have been hypothyroid for only a few months. Titrate dose every 6 weeks. Average full replacement dose is 100-125 mcg/day for a 70 kg adult; usual doses are ?200 mcg/day; doses ?300 mcg/day are rare (consider poor compliance, malabsorption, and/or drug interactions). Note: For patients >50 years or patients with cardiac disease, refer to Elderly dosing.
Severe hypothyroidism: Initial: 12.5-25 mcg/day; adjust dose by 25 mcg/day every 2-4 weeks as appropriate; Note: Oral agents are not recommended for myxedema (see I.V. dosing).
Subclinical hypothyroidism (if treated): 1 mcg/kg/day
TSH suppression:
Well-differentiated thyroid cancer: Highly individualized; Doses >2 mcg/kg/day may be needed to suppress TSH to <0.1 mU/L. High-risk tumors may need a target level of <0.01 mU/L for TSH suppression.
Benign nodules and nontoxic multinodular goiter: Goal TSH suppression: 0.1-0.5 mU/L (benign nodules) and 0.5-1 mU/L (multinodular goiter)
Elderly: Hypothyroidism:
>50 years without cardiac disease or <50 years with cardiac disease: Initial: 25-50 mcg/day; adjust dose at 6- to 8-week intervals as needed
>50 years with cardiac disease: Initial: 12.5-25 mcg/day; adjust dose by 12.5-25 mcg increments at 4- to 6-week intervals. (Note: Many clinicians prefer to adjust at 6- to 8-week intervals.)
Note: Elderly patients may require <1 mcg/kg/day
I.M., I.V.: Children, Adults, Elderly: Hypothyroidism: 50% of the oral dose
I.V.:
Adults: Myxedema coma or stupor: 200-500 mcg, then 100-300 mcg the next day if necessary; smaller doses should be considered in patients with cardiovascular disease
Elderly: Myxedema coma: Refer to adult dosing; lower doses may be needed
Administration: Oral
Administer in the morning on an empty stomach, at least 30 minutes before food. Tablets may be crushed and suspended in 1-2 teaspoonfuls of water; suspension should be used immediately. Levoxyl® should be administered with a full glass of water to prevent gagging (due to tablet swelling).
Administration: I.V.
Dilute vial with 5 mL normal saline; use immediately after reconstitution; do not mix with other IV fluids
Administration: I.V. Detail
Dilute vial with 5 mL normal saline. Use immediately after reconstitution. I.V. form must be prepared immediately prior to administration. Should not be admixed with other solutions.
Monitoring Parameters
Thyroid function test (serum thyroxine, thyrotropin concentrations), resin triiodothyronine uptake (rT3U), free thyroxine index (FTI), T4, TSH, heart rate, blood pressure, clinical signs of hypo- and hyperthyroidism; TSH is the most reliable guide for evaluating adequacy of thyroid replacement dosage. TSH may be elevated during the first few months of thyroid replacement despite patients being clinically euthyroid. In cases where T4 remains low and TSH is within normal limits, an evaluation of “free” (unbound) T4 is needed to evaluate further increase in dosage
Infants: Monitor closely for cardiac overload, arrhythmias, and aspiration from avid suckling
Infants/children: Monitor closely for under/overtreatment. Undertreatment may decrease intellectual development and linear growth, and lead to poor school performance due to impaired concentration and slowed mentation. Overtreatment may adversely affect brain maturation, accelerate bone age (leading to premature closure of the epiphyses and reduced adult height); craniosynostosis has been reported in infants. Treated children may experience a period of catch-up growth. Monitor TSH and total or free T4 at 2 and 4 weeks after starting treatment; every 1-2 months for first year of life; every 2-3 months during years 1-3; every 3-12 months until growth completed.
Adults: Monitor TSH every 6-8 weeks until normalized; 8-12 weeks after dosage changes; every 6-12 months throughout therapy
Reference Range
Pediatrics: Cord T4 and values in the first few weeks are much higher, falling over the first months and years. ?10 years: ~5.8-11 mcg/dL (SI: 75-142 nmol/L). Borderline low: ?4.5-5.7 mcg/dL (SI: 58-73 nmol/L); low: ?4.4 mcg/dL (SI: 57 nmol/L); results <2.5 mcg/dL (SI: <32 nmol/L) are strong evidence for hypothyroidism.
Approximate adult normal range: 4-12 mcg/dL (SI: 51-154 nmol/L). Borderline high: 11.1-13 mcg/dL (SI: 143-167 nmol/L); high: ?13.1 mcg/dL (SI: 169 nmol/L). Normal range is increased in women on birth control pills (5.5-12 mcg/dL); normal range in pregnancy: ~5.5-16 mcg/dL (SI: ~71-206 nmol/L). TSH: 0.4-10 (for those ?80 years) mIU/L; T4: 4-12 mcg/dL (SI: 51-154 nmol/L); T3 (RIA) (total T3): 80-230 ng/dL (SI: 1.2-3.5 nmol/L); T4 free (free T4): 0.7-1.8 ng/dL (SI: 9-23 pmol/L).
Test Interactions
Many drugs may have effects on thyroid function tests (see Additional Information). Pregnancy, infectious hepatitis, and acute intermittent porphyria may increase TBG concentrations; nephrosis, severe hypoproteinemia, severe liver disease, and acromegaly may decrease TBG concentrations.
Dietary Considerations
Should be taken on an empty stomach, at least 30 minutes before food.
Patient Education
Consult prescriber before taking new medication or herbal products during therapy; some other medications or herbals may cause adverse effects with levothyroxine. Thyroid replacement therapy is generally for life. Take as directed, in the morning 30 minutes before breakfast. Do not take antacids or iron preparations within 8 hours of thyroid medication. Do not change brands and do not discontinue without consulting prescriber. Report chest pain, rapid heart rate, palpitations, heat intolerance, excessive sweating, increased nervousness, agitation, or lethargy.
Geriatric Considerations
Elderly do not have a change in serum thyroxine associated with aging; however, plasma T3 concentrations are decreased 25% to 40% in the elderly. There is not a compensatory rise in thyrotropin suggesting that lower T3 is not reacted upon as a deficiency by the pituitary. This indicates a slightly lower than normal dosage of thyroid hormone replacement is usually sufficient in elderly patients than in younger adult patients. TSH must be monitored since insufficient thyroid replacement (elevated TSH) is a risk for coronary artery disease and excessive replacement (low TSH) may cause signs of hyperthyroidism and excessive bone loss. Some clinicians suggest levothyroxine is the drug of choice for replacement therapy.
Additional Information
Equivalent doses: The following statement on relative potency of thyroid products is included in a joint statement by American Thyroid Association (ATA), American Association of Clinical Endocrinologists (AACE) and The Endocrine Society (TES): For purposes of conversion, levothyroxine sodium (T4) 100 mcg is usually considered equivalent to desiccated thyroid 60 mg, thyroglobulin 60 mg, or liothyronine sodium (T3) 25 mcg. However, these are rough guidelines only and do not obviate the careful re-evaluation of a patient when switching thyroid hormone preparations, including a change from one brand of levothyroxine to another. Joint position statement is available at http://www.thyroid.org/professionals/advocacy/04_12_08_thyroxine.html.
Note: Several medications have effects on thyroid production or conversion. The impact in thyroid replacement has not been specifically evaluated, but patient response should be monitored:
Methimazole: Decreases thyroid hormone secretion, while propylthiouracil decrease thyroid hormone secretion and decreases conversion of T4 to T3.
Beta-adrenergic antagonists: Decrease conversion of T4 to T3 (dose related, propranolol ?160 mg/day); patients may be clinically euthyroid.
Iodide, iodine-containing radiographic contrast agents may decrease thyroid hormone secretion; may also increase thyroid hormone secretion, especially in patients with Graves' disease.
Other agents reported to impact on thyroid production/conversion include aminoglutethimide, amiodarone, chloral hydrate, diazepam, ethionamide, interferon-alpha, interleukin-2, lithium, lovastatin (case report), glucocorticoids (dose-related), mercaptopurine, sulfonamides, thiazide diuretics, and tolbutamide.
In addition, a number of medications have been noted to cause transient depression in TSH secretion, which may complicate interpretation of monitoring tests for levothyroxine, including corticosteroids, octreotide, and dopamine. Metoclopramide may increase TSH secretion
Anesthesia and Critical Care Concerns/Other Considerations
Equivalent doses: The following statement on relative potency of thyroid products is included in a joint statement by American Thyroid Association (ATA), American Association of Clinical Endocrinologists (AACE), and The Endocrine Society (TES): For purposes of conversion, levothyroxine sodium (T4) 100 mcg is usually considered equivalent to desiccated thyroid 60 mg, thyroglobulin 60 mg, or liothyronine sodium (T3) 25 mcg. However, these are rough guidelines only and do not obviate the careful re-evaluation of a patient when switching thyroid hormone preparations, including a change from one brand of levothyroxine to another. Joint position statement is available at http://www.thyroid.org/professionals/advocacy/04_12_08_thyroxine.html.
Note: Several medications have effects on thyroid production or conversion. The impact in thyroid replacement has not been specifically evaluated, but patient response should be monitored:
Methimazole: Decreases thyroid hormone secretion, while propylthiouracil decrease thyroid hormone secretion and decreases conversion of T4 to T3.
Beta-adrenergic antagonists: Decrease conversion of T4 to T3 (dose related, propranolol ?160 mg/day); patients may be clinically euthyroid.
Iodide, iodine-containing radiographic contrast agents may decrease thyroid hormone secretion; may also increase thyroid hormone secretion, especially in patients with Graves' disease.
Other agents reported to impact on thyroid production/conversion include aminoglutethimide, amiodarone, chloral hydrate, diazepam, ethionamide, interferon-alpha, interleukin-2, lithium, lovastatin (case report), glucocorticoids (dose-related), mercaptopurine, sulfonamides, thiazide diuretics, and tolbutamide.
In addition, a number of medications have been noted to cause transient depression in TSH secretion, which may complicate interpretation of monitoring tests for levothyroxine, including corticosteroids, octreotide, and dopamine. Metoclopramide may increase TSH secretion
Soy protein may interfere with absorption of levothyroxine sodium. An enteral formula without soy protein should be selected and thyroid function monitored during tube feeding.
Cardiovascular Considerations
The treatment of patients with combined hypothyroidism and ischemic heart disease needs to be approached very carefully, preferably under the guidance of an endocrinologist and cardiologist. This is because administration of substantial doses of thyroid hormone may precipitate acute cardiac ischemia in patients who have been chronically hypothyroid. Therefore, recognizing that dosing regimens may vary, the general approach is to start at very low doses of thyroid supplementation with very gradual increases in dosage every 3-6 weeks. It is important that patients be monitored very carefully for development of cardiac ischemia during thyroid hormone supplementation. Similarly, patients with heart failure and hypothyroidism should be closely followed.
The possibility of underlying hypothyroidism (and also hyperthyroidism) should be considered in patients with atrial fibrillation. Correction of the underlying thyroid disorder may help in restoration of normal sinus rhythm. Hypothyroidism may also constitute an underlying etiology for obstructive sleep apnea.
Dental Health: Effects on Dental Treatment
No significant effects or complications reported
Dental Health: Vasoconstrictor/Local Anesthetic Precautions
No precautions with vasoconstrictor are necessary if patient is well controlled with levothyroxine
Mental Health: Effects on Mental Status
May rarely cause nervousness or insomnia
Mental Health: Effects on Psychiatric Treatment
Used to augment antidepressants; TCAs may increase toxic potential of both drugs
Nursing: Physical Assessment/Monitoring
Use with caution in presence of cardiovascular disease, adrenal insufficiency, diabetes mellitus. Assess potential for interactions with other pharmacological agents patient may be taking (eg, toxic effects with some anorectic drugs, decreased effect of oral hypoglycemics, decreased or increased effect of levothyroxine). Assess results of laboratory tests, therapeutic benefits, and adverse effects on a regular basis during therapy (eg, hypo-/hyperthyroidism). Important: Many drugs may have effects on thyroid function tests and results of laboratory tests. Teach patient proper use, possible side effects/appropriate interventions, and adverse symptoms to report.
Dosage Forms
Excipient information presented when available (limited, particularly for generics); consult specific product labeling.
Capsule, soft gelatin, as sodium:
Tirosint™: 13 mcg, 25 mcg, 50 mcg, 75 mcg, 100 mcg, 125 mcg, 150 mcg
Injection, powder for reconstitution, as sodium: 0.2 mg, 0.5 mg
Tablet, as sodium: 25 mcg, 50 mcg, 75 mcg, 88 mcg, 100 mcg, 112 mcg, 125 mcg, 137 mcg, 150 mcg, 175 mcg, 200 mcg, 300 mcg
Levothroid®: 25 mcg, 50 mcg, 75 mcg, 88 mcg, 100 mcg, 112 mcg, 125 mcg, 137 mcg, 150 mcg, 175 mcg, 200 mcg, 300 mcg
Levoxyl®: 25 mcg, 50 mcg, 75 mcg, 88 mcg, 100 mcg, 112 mcg, 125 mcg, 137 mcg, 150 mcg, 175 mcg, 200 mcg
Synthroid®: 25 mcg, 50 mcg, 75 mcg, 88 mcg, 100 mcg, 112 mcg, 125 mcg, 137 mcg, 150 mcg, 175 mcg, 200 mcg, 300 mcg
Unithroid®: 25 mcg, 50 mcg, 75 mcg, 88 mcg, 100 mcg, 112 mcg, 125 mcg, 150 mcg, 175 mcg, 200 mcg, 300 mcg
Pricing: U.S. (www.drugstore.com)
Tablets (Levothroid)
25 mcg (30): $14.99
50 mcg (30): $13.99
75 mcg (30): $14.99
88 mcg (30): $14.99
112 mcg (30): $14.99
125 mcg (30): $15.99
137 mcg (30): $14.99
150 mcg (30): $15.99
175 mcg (30): $15.99
200 mcg (30): $16.99
300 mcg (30): $20.78
Tablets (Levothyroxine Sodium)
25 mcg (30): $12.99
50 mcg (30): $8.99
75 mcg (30): $12.99
88 mcg (30): $14.99
100 mcg (30): $14.99
112 mcg (30): $12.44
125 mcg (30): $10.99
137 mcg (30): $12.45
150 mcg (30): $10.99
175 mcg (30): $14.99
200 mcg (30): $16.99
300 mcg (30): $18.99
Tablets (Levoxyl)
25 mcg (30): $16.99
50 mcg (30): $17.99
75 mcg (30): $18.99
88 mcg (30): $19.99
100 mcg (30): $17.99
112 mcg (30): $19.99
125 mcg (30): $19.99
137 mcg (30): $19.99
150 mcg (30): $19.99
175 mcg (30): $20.99
200 mcg (30): $21.99
Tablets (Synthroid)
25 mcg (30): $19.99
50 mcg (30): $20.99
75 mcg (30): $23.99
88 mcg (30): $22.99
100 mcg (30): $22.99
112 mcg (30): $23.99
125 mcg (30): $26.99
137 mcg (30): $27.99
150 mcg (30): $25.99
175 mcg (30): $37.99
200 mcg (30): $30.99
300 mcg (30): $38.99
Tablets (Unithroid)
25 mcg (30): $16.99
50 mcg (30): $16.99
75 mcg (30): $17.99
100 mcg (30): $17.99
112 mcg (30): $19.99
125 mcg (30): $19.99
150 mcg (30): $20.99
175 mcg (30): $21.99
200 mcg (30): $21.99
References
Bauer LA, “Simulations of Levothyroxine Bioavailability Using a Single Dose Protocol,” Am J Ther, 1995, 2:414-6.
Berkner PD, Starkman H, and Person N, “Acute L-Thyroxine Overdose: Therapy With Sodium Ipodate: Evaluation of Clinical and Physiologic Parameters,” J Emerg Med, 1991, 9(3):129-31.
Binimelis J, Bassas L, Marruecos L, et al, “Massive Thyroxine Intoxication: Evaluation of Plasma Extraction,” Intensive Care Med, 1987, 13(1):33-8.
de Groot JW, Zonnenberg BA, Plukker JT, et al, "Imatinib Induces Hypothyroidism in Patients Receiving Levothyroxine," Clin Pharmacol Ther, 2005, 78(4):433-8.
Escalante DA, Arem N, and Arem R, “Assessment of Interchangeability of Two Brands of Levothyroxine Preparations With a Third-Generation TSH Assay,” Am J Med, 1995, 98(4):374-8.
Gorman RL, Chamberlain JM, Rose SR, et al, “Massive Levothyroxine Overdose: High Anxiety - Low Toxicity,” Pediatrics, 1988, 82(4):666-9.
Helfand M and Crapo LM, “Monitoring Therapy in Patients Taking Levothyroxine,” Ann Intern Med, 1990, 113(6):450-4.
Johnson DG and Campbell S, “Hormonal and Metabolic Agents,” Geriatric Pharmacology, Bressler R and Katz MD, eds, New York, NY: McGraw-Hill, 1993, 427-50.
Kulig K, Golightly LK, and Rumack BH, “Levothyroxine Overdose Associated With Seizures in a Young Child,” JAMA, 1985, 254(15):2109-10.
Mandel SH, Magnusson AR, Burton BT, et al, “Massive Levothyroxine Ingestion: Conservative Management,” Clin Pediatr (Phila), 1989, 28(8):374-6.
Mayor GH, Orlando T, and Kurtz N, “Limitations of Levothyroxine Bioequivalence Evaluation: Analysis of an Attempted Study,” Am J Ther, 1995, 2:417-32.
Sanders LR, “Pituitary, Thyroid, Adrenal and Parathyroid Diseases in the Elderly,” Geriatric Medicine, 1990, 475-87.
Sawin CT, Geller A, Hershman JM, et al, “The Aging Thyroid. The Use of Thyroid Hormone in Older Persons,” JAMA, 1989, 261(18):2653-5.
Singh N, Singh P, and Hershman J. “Effect of Calcium Carbonate on the Absorption of Levothyroxine,” JAMA, 2000, 283:2822-25.
Stockley IH, Drug Interactions, 5th ed, London, UK: Pharmaceutical Press, 1999.
Tunget CL, Clark RF, Turchen SG, et al, “Raising the Decontamination Level for Thyroid Hormone Ingestions,” Am J Emerg Med, 1995, 13(1):9-13.
Watts NB, “Use of a Sensitive Thyrotropin Assay for Monitoring Treatment With Levothyroxine,” Arch Intern Med, 1989, 149(2):309-12.
International Brand Names
Lexi-Comp.com
Last full review/revision September 2008
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